title: First-principles modelling of magnesium titanium hydrides.
abstract: Mixing Mg with Ti leads to a hydride Mg(x)Ti((1 - x))H(2) with markedly improved (de)hydrogenation properties for x ≤ 0.8, as compared to MgH(2). Optically thin films of Mg(x)Ti((1 - x))H(2) have a black appearance, which is remarkable for a hydride material. In this paper we study the structure and stability of Mg(x)Ti((1 - x))H(2), x = 0-1 by first-principles calculations at the level of density functional theory. We give evidence for a fluorite to rutile phase transition at a critical composition x(c) = 0.8-0.9, which correlates with the experimentally observed sharp decrease in (de)hydrogenation rates at this composition. The densities of states of Mg(x)Ti((1 - x))H(2) have a peak at the Fermi level, composed of Ti d states. Disorder in the positions of the Ti atoms easily destroys the metallic plasma, however, which suppresses the optical reflection. Interband transitions result in a featureless optical absorption over a large energy range, causing the black appearance of Mg(x)Ti((1 - x))H(2).
authors.affiliation: Computational Materials Science, Faculty of Science and Technology and MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Süleyman
authors.initials: S
authors.lastname: Er
authors.forename: Michiel J
authors.initials: MJ
authors.lastname: van Setten
authors.forename: Gilles A
authors.initials: GA
authors.lastname: de Wijs
authors.forename: Geert
authors.initials: G
authors.lastname: Brocks
mesh_terms: D006859:Hydrogen / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D008956:Models, Chemical; D044367:Phase Transition; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D006859:Hydrogen; D014025:Titanium; D008274:Magnesium